Study On Foams With A Dual Network Of Interconnected Pores And Internal Channels And Microwave Foaming

Porous materials have a broad application in areas such as bioengineering,energy and environmental science.And as a novel porous material,foamed microcapillary film(FMCF)is favoured in applications such as tissue engineering scaffolds,wound repair,intelligent water treatment and sustained drug release.In this paper,We first developed liquid-assisted microcapillary film(MCF)extrusion technology.Then batch foaming and microwave foaming technology were studied and further combined with MCF to prepare a novel structure with a dual-pore network of interconnected pores and internal channels.We mainly did the following research:(1)Developed a liquid-assisted microcapillary film(MCF)extrusion method using an improved die structure,which can separately control the forming of each capillary.Experiments proved that the cross-section area of the microcapillaries could be accurately estimated based on the volume flow rate of injected liquid,and its ratio of long axis to short axis decrease with the increase of the volume flow rate of injected liquid,which can be adjusted within 2 ～ 8.The fabricated MCF can carry different kinds/volumes of liquids within its capillaries as it is extruded.(2)FMCF are prepared based on poly(lactic acid)using the batch foaming method.The critical foaming temperature that can maintain the structural integrity of microcapillaries within FMCF were determined for foaming pressure between 13 MPa to 17 MPa,and the effects of the foaming condition on the FMCF foaming behaviour were also investigated.Furthermore,by plugging the ends of the MCF before foaming,the formation of a solid skin layer is successfully avoided,and the diameter of the microcapillaries can be adjusted between 100 μm to 360 μm using a designed foaming strategy.(3)A novel MCF foaming method was studied.We investigated the microwave foaming process and divided it into three stages: energy accumulating stage,pores nucleating and growing stage and periodical collapsing and growing stage,and we also discussed the pore nucleating,growing,collapsing and stabilizing mechanism.The influence of microwave power,the relative water content of the samples and the adding of a nucleating agent on cell morphology were also studied,and we successfully fabricated FMCF via microwave foaming method.